The invention concerns guides in general and more particularly a guide formed from a multistrand spring sheath intended to be introduced into a blood-vessel of narrow diameter so as to allow the introduction of a catheter.
This type of sheath has many applications, notably in the field of cardiovascular surgery such as, for example, during a coronary angioplasty during which a catheter is introduced into a narrow region of the coronary artery of the patient and is inflated to dilate this narrow region.
From the document U.S. Pat. No. 4,548,206 a catheter guide is known which is intended to be introduced by an intravascular path into the human body.
According to this document, the guide comprises a wire or mandril having a proximal part of constant diameter and a tapered distal region. A sheath, formed from a monostrand helicoidal spring having an interior diameter approximately equal to the diameter of the proximal part of the wire, is threaded onto the wire. The proximal extremity of the wire is fixed to the proximal extremity of the spring by a brazed joint and the distal extremity of the wire is left free in the distal region of the spring. Finally, the guide comprises a safety wire formed by a narrow wire which passes along the length of the spring through its interior, and which is also fixed at its two extremities by a brazed joint. The function of the safety wire is to maintain the cohesion of the spring windings and avoid its dislocation when it is submitted to traction.
However, taking into account the very small diameter of these guides, in the order of 0.5 mm, and its relatively important length (as long as 2 m), these guides have a great flexibility which makes them fragile and delicate to manipulate, store and transport.
In fact, it has been observed that during the manipulation and transportation of these sheaths, a great number of them have undergone deformations and notably the dislocation of the windings, which results in them being unsuitable for use.
In fact, such a dislocation forms an extra thickness which reduces or even blocks the sliding of the catheter in the guide.
Furthermore, the need to prepare the safety wire, which must be successively drawn to a convenient diameter in order to then be covered, dressed, cut to length, fettled, and then washed, before being introduced manually in the sheaths and soldered, makes the fabrication costly and time consuming.
It should also be noted that the cross section of the safety wire is very small (1,4.times.10.sup.-2 mm) and that the resistance of its fastenings is weak. It can thus easily be seen that an incorrect manipulation of the guide can easily lead to traction on the safety wire, resulting in its rupture. Such a rupture can cause the unwinding of the spring which, if occurring in a vein of a patient, can cause serious complications notably during its extraction.